This invention relates to a signal transmission device for converting a physical quantity developed within the rotor of an electric rotary machine such as an AC generator or an AC motor to an electrical signal and transmitting it to the stationary side of the machine in a contact-less manner.
In the signal transmition such as above described, the transmitting antenna disposed on the rotor is of the electromagnetic induction type and the receiving antenna disposed on the stator is in the form of a loop of the electromagnetic induction type disposed to have a sufficient electromagnetic coupling to the electromagnetic induction type transmitting antenna at any angular position of rotation of the rotor. Then it is a common practice to transmit a plurality of types of signals according to either a frequency division system using different carrier waves or subcarrier waves different from one another and forming a common carrier wave or to a time sharing system using a single carrier wave. When the plurality of types of the signal are expressed by respective digital codes each put in the form of serial bits and transmitted in the time sharing manner to the stator, it is necessary to use only a single transmitting device.
However, in order to easily obtain excellent dynamic balance in rotors it is desirable to form the transmitting device of a pair of units identical in construction to each other. On the other hand, in case of the transmission of digital signals in the form of serial bits, is it necessary to transmit a frame or a word synchronizing signal for each digital signal. The transmission of this synchronizing signal along a channel different that of the digital signal in many cases permits the simplification of the resulting device. There have not been any previously proposed signal transmission devices optimum for meeting the requirements as described above.
Accordingly, it is an object of the present invention to provide a new and improved signal transmission device for transmitting a data signal representing, for example, the field voltage, the current etc. of the rotor of an electric rotary machine externally of the rotor while the rotor is rotated.